-Where have you been?......

-Where have you been?
-I've been to the post office-I _____ post a letter.
A.must
B.ought to
C.had to
D.need

请问是选D吗？如果不是那选什么为什么？
~~(╯﹏╰)b不会吧！~寄信是过去的动作，所以要用had to？为什么啊？这里考察情态动词啊！~

Where have you been? where have you gone是什么意思 Where have you been hiding where have you been where did you go的区别 where have you gone与 where did you go 与 where were you 与 where have you been ---- where have you ____ these days? where did you have your supper?- ____ where have you been up to? where have you put the box where else have you observed colorful light emissions?